Read here. With the advancement of paleo-climate science in recent years, the empirical evidence clearly indicates that Penn State's Michael Mann 'hockey stick' temperature graph to be without merit. The hockey-stick scenario was so discredited that even the IPCC eliminated it from their 2007 report.

Yet the hockey-stick myth continues to survive as a green legend despite the mounting empirical evidence that the Medieval Global Warming remains unprecedented.

Indeed, as the adjacent chart indicates, the Medieval Warming was significantly higher than the current warming.

Abrantes et al. just published research revealing the persistent high Medieval temperatures of coastal waters off the Portugal coast. Their analysis (from 900 AD to year 2002) is based on a sediment core from the Atlantic Ocean seabed.

As can be seen, levels of atmospheric CO2 have had little, if any, impact on sea surface temperatures. And this specific research clearly indicates that as CO2 levels rose, the SSTs declined - opposite of IPCC's climate model predictions.

"Abrantes et al. reconstructed a sea surface temperature (SST) history for waters off the coast of Porto, Portugal covering the past thousand years...revealed the occurrence of the Little Ice Age, as well as what they describe as the "persistently higher temperatures registered in the AD 960-1300 interval that we identify as the MWP [ed: Medieval Warming Period]." And from a graph of their SST history, one can see that the peak warmth of the MWP was about 1.2°C greater than the peak warmth of the CWP during the late 20th century." [F. Abrantes, T. Rodrigues, B. Montanari, C. Santos, L. Witt, C. Lopes, A. H. L. Voelker 2011: Climate Research]